1. Field of the Invention
This invention relates to an apparatus for detecting the occurrence of a misfire in an internal combustion engine such as a multi-cylinder internal combustion engine.
2. Description of the Related Art
Japanese published unexamined patent application 4-365958 corresponding to U.S. Pat. No. 5,275,037 discloses an apparatus for detecting the occurrence of a misfire in an internal combustion engine. The apparatus of Japanese application 4-365958 responds to a rotation signal which is output from a rotational angle sensor in accordance with the rotation of the crankshaft of the engine at every predetermined rotational angle of the engine crankshaft. In addition, the apparatus successively calculates an amount of time taken for revolution of the engine crankshaft by a predetermined crank angle on the basis of the rotation signals. The apparatus then sets first and second decision values on the basis of the calculated times in connection with two cylinders of the engine which successively take explosion strokes. The second decision value is set at a timing of 360 degrees in the engine crankshaft rotational angle previous to a timing of the setting of the first decision value. The occurrence of a misfire is detected on the basis of the first and second decision values.
Japanese published unexamined patent application 5-149191 corresponding to U.S. Pat. No. 5,287,736 discloses a misfire detecting apparatus for a multi-cylinder internal combustion engine. In the apparatus of Japanese application 5-149191, a rotation signal outputting unit outputs a rotary signal at every predetermined rotary angle, and a tentative misfire decision unit tentatively decides, on the basis of the rotary signal, whether or not misfire has occurred in each of cylinders of the engine. In addition, a tentative misfire number counting unit counts the number of tentative misfires decided for the respective cylinders, and a counting result storage unit stores the counting results. After a given number of tentative misfire decisions have been made, it is decided that a misfire has actually occurred only if the counting result, for a part of the cylinders, among the counting results for the respective cylinders stored in the counting result storage unit is larger than a predetermined number.